Human color vision is trichromatic, we use three pigments (blue, green and red) to discriminate different colors. Inherited red/green color vision deficiencies are X-linked and occur with a rather high frequency (about 8%) in the male population. These inherited deficiencies are thought to arise by homologous recombination between the highly homologous red and green genes which are both located on the X chromosome. Although this is supported by much genetic evidence, the isolated pigments were not heretofore available to test this model directly. The broad aim of the research outlined in this proposal is to elucidate the structure, spectral properties, and mechanism of action of the human color vision pigments, and to test molecular models for inherited human color vision deficiencies. The experimental approach will be to use site-directed mutagenesis in combination with mammalian cell culture to produce the human pigments. The wild-type and modified pigments will be purified to homogeneity and characterized in vitro. There are two specific goals. First is to test the hypothesis that human red/green color vision deficiencies arise by unequal homologous recombination events. Second is to characterize the isolated human color vision pigments in terms of their general spectral and biochemical properties.